Safety device for gas lift well

ABSTRACT

For use in a well where production is sustained through gas lift methods, an apparatus which shuts in the well on catastrophic failure. The apparatus includes a set of spaced, slidably mounted pistons carried on the production tubing string. Openings in the pistons permit gas flow down through the pistons. When gas flow is upward in the annulus, the lower piston is lifted upwardly and contacts the centrally located piston. The pair slide upwardly against the topmost piston, which is fixedly mounted. When pressed together, the openings through the pistons do not permit continued gas flow in the annulus. This closes the annulus to gas flow.

United States Patent 1 11 3,724,541 Curry Apr. 3, 1973 [54] SAFETY DEVICE FOR GAS LIFT WELL [76] Inventor: David B. Curry, PO. Box 405, Primary Examinernjames A'Leppink Woodville, Tex. 75979 Ammekmmld [22] Filed: Mar. 22, 1971 [57] ABSTRACT [21] Appl.No.: 126,616 For use in a well where production is sustained through gas lift methods, an apparatus which shuts in the well on catastrophic failure. The apparatus in- [52] US. Cl ..l66/224 cludes a set of spaced, slidably mounted pistons can Illt. Clq ..E2lb l ied on the du t on tub n strin 0 i s i h 58 Field of Search ..l66/224 176 t g p g pistons permit gas flow down throughthe pistons. Whengas flow is upward in the annulus, the lower [56] References Cited piston is lifted upwardly and contacts the centrally UNITED STATES PATENTS located pis ton. The pair slide upwardly against the topmost piston, which IS fixedly mounted. When 3,330,359 7/1967 Ward ..166/176 pressed together, the openings through the pistons do 3,273,648 /1 B rn r not permit continued gas flow in the annulus. This 3,570,597 3/197l Lack closes the annulus to gas flow. 3,537,519 ll/l970 Long 3,330,358 7/1967 Ward ..l66/176 8 Claims, 5 Drawing Figures PATENTEDAPR 3 ma David 5. Curry INVENTOR Donald Gunn ATTORNEY SAFETY DEVICE FOR GAS LIFT WELL SUMMARY OF PROBLEM AND SOLUTION Production in oil wells is commonly by a pump or gas lift method. In deep wells, pumping is not routinely used because the extensibility of the sucker rods deprives the pump of a sufficient stroke. In such cases, gas lift is used. In gas lift methods of production, a

production string is installed within the cased opening.

Production is attained through this production tubing. The annulus outside the production string, but within the cased hole, is used as the downward path of communication for the gas which is used in the gas lift equipment. Gas under high pressure is forced into the annulus, and is introduced into the production or tubing string to reduce the density of petroleum products derived from a deep formation so that they rise in the production string. Hence, gas lift valves are installed at various elevations within a well, and are adjusted to introduce a certain rate of lifting gas into the production string whereby the liquid therebelow is lifted even higher in the well.

Gas lift wells are subject to certain catastrophic failures. For instance, the rupture of the casing might well lead to catastrophic failure. Failure of the well head apparatus would also be considered a catastrophic failure. Other modes and forms of failure are equally likely to arise. In offshore production, a hurricane or high sea might relocate or otherwise damage a production platform. This typically will snap off the production tubing in the casing somewhere between the bottom of the body of water and the platform itself. In these examples, and in many other cases, safety equipment of the sort which relates to the present invention would be considered very desirable, or even essential. Accordingly, the present invention is summarized as providing a safety device which prevents upward flow in the annulus surrounding a production tubing string. More specifically, the apparatus is-summarized as incorporating a family of serially mounted, slidable pistons carried on the outside of a production tubing string which are spaced from one another during routine operation of the well. When gas flows downwardly through the annulus, it flows through the various pistons through the use of spaced openings in the pistons sufficient for the gas flow. The openings in the various pistons, however, do not coincide with one another in their relative locations. Lower pistons are slidably mounted on the production tubing string and are adapted to slide upwardly and downwardly. In the event of failure of pressure in the annulus, the tendency of upward flow will lift the slidable lower pistons and move them upwardly to the uppermost piston which is held in fixed position. When the pistons contact one another, the openings therein do not match, and the pistons seal one against the other to close to annulus to continued upward fluid flow.

More will be noted concerning the summarized invention upon a reading and consideration of the following specification in conjunction with the drawings, which are: I

FIG. 1 is a sectional view showing a conventional gas lift well which is enhanced with the device of the invention shown in sectional view, and including a plurality of slidable pistons mounted on the production tubing;

FIG. 2 is a view similar to FIG. 1 showing the pistons contacted one against the other after upward flow in the annulus has been initiated as might arise on a catastrophic failure thereabove;

FIG. 3 is a sectional view along the line 3 3 of FIG. 1 illustrating details of construction of a particular piston comprising a portion of the present invention;

FIG. 4 is a sectional view along the line 4 4 of FIG. 1 illustrating details of construction of a particular piston comprising a portion of the present invention; and,

FIG. 5 is a sectional view along the line 5 5 of FIG. 1 illustrating details of construction of a particular piston comprising a portion of the present invention.

In the drawings, attention is directed first to FIG. 1 where the numeral 10 indicates a cased producing well. A single string of production tubing is presumed, and is indicated at 12. The present invention is useable with multiple completions in which event various pistons as will be described have multiple aligned central openings whereby they fit about the production tubing string. However, for sake of clarity, only a single production string is shown in FIG. I. theproduction tubing 12 is of conventional construction and includes a pin and box for connection with the remaining portions of the production string. The production tubing 12 is of conventional construction internally and is simply adapted to communicate the petroleum products upwardly through the tubing string. The safety device of the present invention is indicated generally by the numeral 14. It is preferably installed at two or three spaced locations in a well. While a minimum of one might be adequate, circumstances may dictate the use of more than one safety device. In deep water offshore production, it might be well to install the safety device of the present invention very near the top of the well head, but at a point which would still be in the water. Further, it might be well to install the safety device of the present invention at a second location, perhaps 50 to feet below the mud level at the bottom of the body of water. As will be understood from an explanation of the safety device 14 hereinafter, the failure may be so located as to fall below the first safety device, but still above the second safety device, and thereby obtain protection from it. If unconsolidated formations surround a particular well, it may be apt to locate the safety device even lower in the well in such a case.

The safety device 14 of the present invention requires a modified production tubing member in the following manner. The production tubing member 12 is provided with a lower external collar 16. An upper external shoulder 18 is likewise included. As a matter of convenience, the shoulder 18 may define the box connection of the tubing 12. In any case, an upper shoulder is provided. A metal piston 20 is mounted on the exterior of the tubing member 12. The metal piston 20 is used somewhat as a spacer within the cased hole. As will be observed in the drawings, the member 20 is preferably circular, and preferably centers the production tubing member 12. Of course, the axial opening for the tubing 12 may be located off center as required. In any case, the piston 20 is forced on the exterior of the production tubing 12 and is held in the illustrated position by spot welds or other suitable means. i

The piston has a number of openings drilled in it as indicated in dotted line at 22. The openings 22 are shown better in FIG. 3. They are spaced sufficiently about the circular shaped piston to provide an adequate flow axially of the well. They extend through the piston from the upper to the lower face, as shown in the drawings. The piston has an upper face which is abutted against the shoulder 18. It also has a lower face which is planar, and facing downwardly in the annulus. The lower face is adapted to be contacted against the second and slidable piston 24. The piston 24 is shown in FIG. 1 resting on a shoulder 26. The tubing 12 is somewhat more narrow above the shoulder.26. The

shoulder 26 is sufficiently large to catch and support the slidable piston 24.

The piston 24 is shown in FIG. 4, including a number of splined slots 28. Of particular interest is the fact that the holes 22 in the uppermost piston do not line up with the splined slots 28 in the piston 24. When they are spaced apart as shown in FIG. 1, a suitable gas flow path is provided. However, the mismatch in the location of the openings will be discussed in detail hereinafter when describing the operation of the invention.

It should be noted that the sliding piston 24 is formed of a resilient material, such as hard rubber. The corners are bevelled so that the rubber does not grip too firmly against the casing 12. If desired, the surface can be smooth, or coated with a slick material such as Teflon. Of particular interest is the fact that the upper face of the slidable piston 24 matches the lower face of the fixed piston 20. The two faces are adapted to be contacted one against the other in the closed position of the safety device 14. The piston is of reasonable thickness, perhaps in the range of 2 to 4 inches thick, although the thickness might vary quite widely. It is not necessarily a load bearing member, and hence, it does not require excessive structural strength. One requirement as to size and thickness is that the slidable piston have adequate strength and thickness to maintain structural integrity.

As shown in FIG. 1, the piston 24 rests on a shoulder 26 at a midpoint along the tubing 12. The piston 20 is at the upper end. An additional and last piston 30 is rested on the collar or shoulder 16. It, too, is slidably received on the exterior of the tubing 12. The piston 30 is also concentrically positioned about the tubing string 12. The piston 30 is of metallic construction and has a plurality of openings indicated'at 32 in FIG. 5. The cross sectional area of the openings extending through the various pistons as shown in FIGS. 3, 4 and 5, is approximately equal to one another. This will prevent any one of the several pistons from serving as a choke or bottleneck in the gas passage in the annulus. More particularly, the openings in the bottommost piston 30 again do not match or coincide with the openings in the central piston. Thus, when the pistons 24 and 30 are spaced from one another as shown in FIG. 1, the high pressure gas flows downwardly through the annulus somewhat in the manner indicated by the arrows in FIG. 1.

The piston 30 is slidably rested on the shoulder 16. It is adapted to be moved upwardly. The fit about the tubing 12 need not be too close, and is sufficiently loose to permit the piston 30 to slide upwardly over the shoulder 26, and to also fall down and pass the shoulder when returning to its original non-operated position of FIG. 1.

The piston 30 has sufficient width at the line of contact with the casing 10 to maintain the piston in a generally horizontal posture, to prevent it from canting or tilting as it slides upwardly and downwardly. This generally serves to keep the piston aligned with the tubing 12.

Attention is redirected to FIG. 1 of the drawings which shows the apparatus in the installed posture, but before operation. During its customary use, gas under high pressure is forced downwardly through the annulus and passes through the three pistons, using the drilled passages shown in FIGS. 3, 4, and 5. Its flow continues unabated, and is not particularly impeded by the safety device of the present invention. The pistons 24 and 30 are at the downward positions, positioned there by gravity, and remain in these positions so long as the gas flow is downward.

Suppose, for sake of description, that a catastrophic failure such as a rupture of the casing occurs at some point above the safety device 14. In such event, pressure in the annulus will drop close to zero. The pressure drop reverses the flow in the annulus. The volume of the annulus below the safety device is quite measurable, especially on relatively deep wells. The reservoir found in the annulus is therefore quite substantial, and is sufficient to cause upward flow in the annulus. As the direction of flow reverses after the occurrence of catastrophic failure, the pressure drop across the openings in the pistons 30 and 24 acts on them with an upward or lifting force. The pistons 30 and 24 are abutted against shoulders which prevent downward movement, but are slidably received on the tubing string 12 for upward movement. The pressure flow upward in the annulus forces the piston 30 upwardly. The piston 24 also moves upwardly. The result of the movement is illustrated in FIG. 2 wherein the resilient piston 24 moves to the uppermost position while the piston 30 moves as high as possible and abuts against the lower face of the piston 24. The pistons then are contacted against one another. The transverse openings through them which permit gas flow in the annulus do not match up, as shown in FIGS. 3, 4 and 5. The coaction of the metal pistons 20 and 30 with the resilient piston 24 therebetween tends to close off and seal the interfaces between the pistons to prevent leakage from passage to passage. Thus, the annulus is closed to upward gas flow. This traps all of the gas in the annulus, p

and further prevents leakage past the safety device to the point of the catastrophic failure. This may well prevent pollution, dangerous fires, explosions, and the like.

It should be noted that the pistons 24 and 30 require a relatively loose fit within the casing 10. In the event of loss of pressure and movement of the pistons 24 and 30 to the operated position of FIG. 2, the two metal pistons 20 and 30 squeeze the resilient piston 34 and cause it to expand slightly, thereby forming a more perfect seal with the inner wall of the casing .10. When squeezed, the more perfect seal tends to further close off upward communication in the annulus of the well,

and provide a more perfect seal to prevent the continued leakage of petroleum products to the vicinity of the catastrophic failure.

It will be appreciated that the equipment can assume the posture of FIG. 2 for hours, or even days. The movable or slidable pistons remain in the closed position of FIG. 2 indefinitely. This position is continued until such time as the pressure below the slidable piston 30 is reduced. This might be accomplished many weeks later when control over the well is asserted by repair of the catastrophic failure. By way of example, assume that the well head is accidently damaged and knocked away. The repair may require the attachment of a new Christmas Tree to the well. In this event, the new Christmas Tree is attached and thereafter, the gas lift method of production is re-established by pumping gas downwardly through the annulus, as was originally the case. In this event, the gas pressure is forced downwardly in the annulus and enters the openings 22 in the top piston 20. This tends to force the slidable pistons 24 and 30 downwardly. As the differential pressure acting on the lower face drops and reverses itself, the pistons 24 and 30 slide downwardly. The downward movement continues until the pistons 24 and 30 are repositioned on the shoulders 26 and 16, respectively.

At this juncture, the annulus can then be used in the gas lift method of productionindefinitely. The separation of the pistons permits continued gas flow through the tube.

Certain alternative embodiments of the present invention will now be considered. The drawings show the device with a single tubing string for production. Many wells penetrate multiple pay zones, and consequently,

passage through the annulus of the well when said first and second members are contacted against one another; and,

including a third member below said second member, said third member extending substantially transversely and closing the annulus to fluid flow therethrough, said third member having a plurality of passages therethrough serving as passage means communicating from a point above to a point below said. third member in the annulus, said third member being slidably received on a tubing string therein and movable upwardly and downwardly with respect to said second member.

2. The invention of claim 1 including shoulder means located on the tubing string for positioning and receiving thereon said second member, said shoulder means facing upwardly whereby said second member is adapted to be slidably movable upward toward said first member.

3. The invention of claim 1 wherein said passage means in said first member include drilled openings extending from the upper to the lower sides thereof which are located at a predetermined point with respect to the center thereof, and said passage means in said second require two, three, or even four production strings. The

present invention is easily adapted for use with multiple production strings on relocation of the central openings in the several pistons 20, 24 and 30. Again, the device functions in large part by the misalignment of the passages through the several pistons whereby upward gas flow through the annulus is prevented when the pistons are contacted against one another.

Many changes, alterations, and variations can be incorporated within the structure without departing from the scope thereof, which is determined by the claims appended hereto.

What is claimed is: I

1. Safety apparatus for use in a well having a tubing string therein, comprising:

a first transversely extending member adapted to be positioned within a well and extending substantially thereacross, said means having a centrally located opening therein to permit positioning about a tubing string within such a well;

passage means through said first member;

a second member adapted to be slidably positioned about a tubing string in the well and further extending substantially transversely thereof in the annulus of the well, said second member being slidable upwardly in the well toward said first member arranged thereabove;

passage means through said second member;

said passage means in said first member and said second member both being located in and providing a path of communication through the annulus of the well and being non-coincident with one another such that a passage is provided in the annulus of the well when said first and second members are separated one from the other and being further adapted to close the member being located at a point inboard of said passage means in said first member so as to maintain a non-coincident relationship when said first and second members are contacted against one another.

4. The invention of claim 3 wherein said passage second shoulders thereon, said first shoulder facing downwardly and adapted to be contacted against said first member to support said first member at a position for closing the annulus, and wherein said second shoulder isspaced therebelow and said tubing string is of reduced diameter between said first and second shoulders to permit said second member to slide relatively therebetween.

6. The invention of claim 1 wherein the passage means in said third member are non-coincident with the passage means in said second member when said members are contacted against one another.

7. The invention of claim 6 wherein said first and third members are formed of metal while said second member is formed of a resilient material and is com pressable by said first and third members.

8. The invention of claim 1 wherein the safety device of the present invention incorporates a tubing string having first, second and third shoulders, said first shoulder being at an upper point thereof and facing downwardly and adapted to receive thereagainst in a fixed position said first member, said second shoulder being located therebelow and being separated from said first shoulder by a portion of said tubing string of reduced diameter and supporting said second member for slidable movement between said second shoulder toward said first shoulder for abutting contact against said first member, and wherein said third shoulder is below. said second shoulder, there being a portion of said tubing string between said second and third shoulders of reduced diameter greater than that above said second shoulder, and adapted to receive for slidable movement thereon said third member from a position resting on said third shoulder upwardly past said 

1. Safety apparatus for use in a well having a tubing string therein, comprising: a first transversely extending member adapted to be positioned within a well and extending substantially thereacross, said means having a centrally located opening therein to permit positioning about a tubing string within such a well; passage means through said first member; a second member adapted to be slidably positioned about a tubing string in the well and further extending substantially transversely thereof in the annulus of the well, said second member being slidable upwardly in the well toward said first member arranged thereabove; passage means through said second member; said passage means in said first member and said second member both being located in and providing a path of communication through the annulus of the well and being non-coincident with one another such that a passage is provided in the annulus of the well when said first and second members are separated one from the other and being further adapted to close the passage through the annulus of the well when said first and second members are contacted against one another; and, including a third member below said second member, said third member extending substantially transversely and closing the annulus to fluid flow therethrough, said third member having a plurality of passages therethrough serving as passage means communicating from a point above to a point below said third member in the annulus, said third member being slidably received on a tubing string therein and movable upwardly and downwardly with respect to said second member.
 2. The invention of claim 1 including shoulder means located on the tubing string for positioning and receiving thereon said second member, said shoulder means facing upwardly whereby said second member is adapted to be slidably movable upward toward said first member.
 3. The invention of claim 1 wherein said passage means in said first member include drilled openings extending from the upper to the lower sides thereof which are located at a predetermined point with respect to the center thereof, and said passage means in said second member being located at a point inboard of said passage means in said first member so as to maintain a non-coincident relationship when said first and second members are contacted against one another.
 4. The invention of claim 3 wherein said passage means in said second member include centrally axially located slots.
 5. The invention of claim 1 wherein the tubing string is incorporated as a portion of the safety device of the present invention, and further including first and second shoulders thereon, said first shoulder facing downwardly and adapted to be contacted against said first member to support said first member at a position for closing the annulus, and wherein said second shoulder is spaced therebelow and said tubing string is of reduced diameter between said first and second shoulders to permit said second member to slide relatively therebetween.
 6. The inventioN of claim 1 wherein the passage means in said third member are non-coincident with the passage means in said second member when said members are contacted against one another.
 7. The invention of claim 6 wherein said first and third members are formed of metal while said second member is formed of a resilient material and is compressable by said first and third members.
 8. The invention of claim 1 wherein the safety device of the present invention incorporates a tubing string having first, second and third shoulders, said first shoulder being at an upper point thereof and facing downwardly and adapted to receive thereagainst in a fixed position said first member, said second shoulder being located therebelow and being separated from said first shoulder by a portion of said tubing string of reduced diameter and supporting said second member for slidable movement between said second shoulder toward said first shoulder for abutting contact against said first member, and wherein said third shoulder is below said second shoulder, there being a portion of said tubing string between said second and third shoulders of reduced diameter greater than that above said second shoulder, and adapted to receive for slidable movement thereon said third member from a position resting on said third shoulder upwardly past said second shoulder. 